A COA technology refers to a technology where a color filter layer is directly formed on an array substrate, and the resultant array substrate is called as COA substrate. For a COA display panel, it is unnecessary to align a color filter substrate with the array substrate, so it is able to prevent the occurrence of an error in the related art where the color filter substrate is arranged opposite to the array substrate to form a cell. At this time, a narrow black matrix may be provided, so as to improve an aperture ratio of a pixel.
However, along with the improvement of a resolution of a liquid crystal display device, a smaller size of a pixel unit for the display panel is required. In the related art, a via-hole in the color filter substrate is of a large size, so a size of a drain electrode of a transistor on the array substrate is relatively large too, and thereby the aperture ratio of the pixel will be adversely affected. In addition, light at a side of the via-hole may be reflected by the large drain electrode, and as a result, light leakage will occurs for the liquid crystal display device and a display effect thereof will be adversely affected.